How are zinc ores concentrated before metal extraction?

Because zinc ores typically contain only a small fraction of zinc sulfide minerals, they must undergo beneficiation to create a concentrate suitable for further treatment. The primary method used for this concentration is flotation separation.1

The process involves the following steps:

• Crushing and Grinding: The ore is first crushed to approximately 1.9 centimetres (0.75 inch) and then ground in a ball mill until the particles are less than 0.1 millimetre in size.1
• Slurry Formation: The finely ground ore is mixed with water to create a slurry.1
• Flotation: The slurry is moved to flotation cells or tanks where chemical reagents are added. The mixture is agitated by beaters while air bubbles are introduced.1
• Separation: The zinc mineral particles attach to the air bubbles and rise to the surface as an oily froth, which is then skimmed off. Meanwhile, the unwanted material, known as gangue, is wetted by the chemicals and sinks to the bottom of the cell.1

This process allows for the effective isolation of zinc sulfide from impure constituents, and the careful selection of frothing agents can even separate complex lead and zinc sulfides into individual concentrates.1